1. Field of the Invention
This invention relates to on-chip power combining for high-power Schottky diode based frequency multipliers.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
High-power sources in the W-band (70-110 GHz) and the F-band (90-140) Gigahertz (GHz) range are in demand for a variety of applications. Most prominently, the sources can be used for terahertz communications [1] and in millimeter- and submillimeter-wave radars or radiometers, which are being considered for security applications such as surveillance, mass transit security, and perimeter intrusion detection. Reaching the highest possible powers is critical for radars that operate at long range, or that require distributing signal power to multiple transmitters and receivers [2]. These systems often benefit by operating within atmospheric absorption windows, which are located around 230, 345, 460, and 690 GHz. Frequency-multiplied Schottky diode sources are a preferred technology to generate relatively high power in the submillimeter-wave ranges; see sources review in [3]. But with efficiencies in the 10% range for submillimeter-wave multipliers, very high-power sources (>100 milliwatts (mW)) around 115 GHz are needed to reach those windows (using multiplication factors of ×2, ×3, ×2×2, and ×2×3 respectively). Multi-pixel terahertz receivers for astrophysics can also benefit from high-power W-band and F-band sources, which require local oscillator power to be distributed among many mixers.
Solid state amplifiers would be a preferable alternative to Schottky diodes for generating power at high frequencies. However, there are currently no commercially available amplifiers that extend beyond 110 GHz (several do reach the 100-110 GHz band, for example HRL [4] and Millitech [5]). Years ago, TRW fabricated amplifiers that work up to 120 GHz for the Herschel Space Observatory [6], but these are no longer available or offered for sale. Amplifier technology is progressing fast and power levels of 50 mW have been demonstrated at 220 GHz using InP transistors [7], but only by power-combining eight amplifiers, which has a clear impact on complexity and cost.